Offering Salah while sitting

Q 2: For a long period of time I have been performing all daily obligatory five Salahs (Prayers) while sitting. Is this valid? Give me a Fatwa (legal opinion), may Allah reward you well, on whether to observe Sawm (Fast) or offer Fidyah (ransom) and on performing Salah while sitting, may Allah bless you! (Part No. 6; Page No. 365

Standing when able to do so is one of the pillars of Salah without which Salah will not be valid. However, if you are unable to stand, it will be permissible for you to offer Salah while sitting. To this effect, the Prophet (peace be upon him) said to `Imran ibn Al-Husayn (may Allah be pleased with him): “Offer Salah standing and if you cannot, then sitting; and if you cannot, then lying on your side.” (Related by Al-Bukhari and others) It is also related by Al-Nasa’y through a trustworthy Isnad (chain of narrators) with the addition: “...And if you cannot, then lying on your back.” If you can sometimes stand, you will then have to do so, because Allah (Glorified be He) says: So keep your duty to Allâh and fear Him as much as you can In the same regard, the Prophet (peace be upon him) said: “When I command you to do something, do of it as much as you can .” (Related by Al-Bukhari and Muslim on the authority of Abu Hurayrah [may Allah be pleased with him])May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.